MFL IMENTS  OF 

THE  AUTHOR 
CAN  AH])  A  T  OVA 

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N.  Y. 


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rom  Vol.  XII,  Transactions  of  American  Ceramic  Society. 
(Read  at  Pittsburgh  Meeting,  February,  1910.) 


METHODS  OF  ANALYSIS  FOR  ENAMEL  AND 
ENAMEL  RAW  MATERIALS. 


BY  / 


ROBERT  D. 


N  DRUM 


5"  ¥ 


METHODS  OF  ANALYSIS  FOR  ENAMEL  AND 
ENAMEL  RAW  MATERIALS. 

BY 

Robert  D.  Landrum,1  Lawrence,  Kansas. 

Introduction.  The  fact  that  practically  nothing  lias 
been  published  on  the  above  subject,  and  the  remembrance 
of  the  many  long  hours  spent  in  digging  out  these  methods 
and  adapting  them  to  enamels  and  enamel  raw  materials, 
has  led  the  author  to  put  them  in  this  form  for  others 
who  might  use  them.  While  he  claims  little  originality 
in  the  methods  themselves,  he  does  claim  originality 
in  the  adaptations  here  given.  Each  and  every  one  of 
these  methods  has  been  thoroughly  tried  out,  either  in  the 
laboratory  of  the  Columbian  Enameling  and  Stamping 
Company,  at  Terre  Haute,  Ind.,  or  in  the  chemical  labora¬ 
tories  of  the  University  of  Kansas. 

PART  I. 

THE  ANALYSIS  OF  AN  ENAMEL. 

The  analysis  of  an  enamel  presents  one  of  the  most 
difficult  and  complicated  problems  with  which  the  analyst 
comes  in  contact.  An  enamel  is  generally  an  insoluble 
silicate  containing  besides  silica,  iron,  alumina,  calcium, 
magnesium  and  the  alkalies,  generally  boron,  fluorine, 

1  This  paper  was  prepared  as  a  thesis  for  the  master’s  degree  at  Rose 
Polytechnic  Institute.  The  author  desires  to  render  thanks  to  Dr.  W.  A. 
Noyes  and  Dr.  John  White,  his  former  instructors,  for  advice  freely  given, 
and  to  Dr.  E.  H.  S.  Bailey  and  Dr.  H.  P.  Cady  for  suggestions  offered. 
Methods,  especially  from  the  following  sources,  have  been  freely  used,  and 
adapted  to  the  specific  uses  herein  described:  Treadwell  and  Hall’s  “Analyti¬ 
cal  Chemistry”;  Classen’s  “Ausgewahlte  Methoden  der  Analytischen  Chemie”; 
Sutton’s  “Volumetric  Analysis”;  Lunge  and  Keane’s  “Technical  Methods  of 
Chemical  Analysis”;  “Methods  of  Agricultural  Analysis”  (Bui.  107,  U.  S. 
Dep’t  of  Agric.);  Hillebrand’s  “Analysis  of  Silicate  Rocks”  (U.  S.  Geol.  Sur¬ 
vey  Bui.  305);  and  the  files  of  the  Journals  of  the  various  Chemical  Societies. 

1 


W 


2  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

manganese,  cobalt,  antimony  and  tin,  and  sometimes  phos¬ 
phorus  and  lead.  Before  attempting  the  quantitative 
analysis  of  any  enamel  a  thorough  qualitative  analysis 
should  be  run,  and  this  will  enable  one  to  choose  a  quanti¬ 
tative  separation.  One  of  the  most  important  aids  to  a 
correct  analysis  is  a  thorough  grinding.  The  sample  should 
be  ground  to  an  almost  impalpable  powder,  and  every 
conceivable  precaution  for  accuracy  taken. 

The  analysis  of  a  sample  of  enamel  to  be  taken  from 
a  piece  of  ware  involves  an  extra  difficulty.  The  coating  of 
enamel  almost  always  consists  of  two  or  more  layers — the 
lower  a  large  ground  coat,  and  the  upper  ones  white  or 
colored  enamels.  For  an  illuminating  analysis  these  must 
be  separated.  The  author  has  found  the  following  method 
of  V.  de  Luyeres1  good  for  doing  this:  The  surface  is 
scratched  lightly  with  a  piece  of  emery  cloth  or  a  file,  and  a 
coating  of  gum  acacia  or  glue  is  applied.  The  vessel  is 
placed  in  an  air-bath  and  heated.  The  glue  on  hardening 
generally  carries  with  it  some  of  the  outer  coat.  The  glue 
or  gum  is  then  broken  off,  dissolved  in  water  and  the  enam¬ 
el  pieces  collected  on  a  filter  paper.  Some  obstinate  enam¬ 
els  require  painstaking  methods,  such  as  chipping  off  with 
a  chisel  and  separating  the  different  coats — which  always 
vary  somewhat  in  color — by  picking  out  and  sorting,  using 
a  pair  of  forceps.  A  large  reading  glass  will  be  useful  in 
making  these  separations.  Any  iron  from  the  vessel  which 
may  adhere  to  the  enamel  may  be  removed  by  means  of  a 
magnet  after  the  sample  is  ground. 

Analysis  of  an  Enamel  Containing  Fluorine. 

In  an  enamel  containing  fluorine  the  usual  methods 
for  silicates  cannot  be  used,  as  silicon-tetra-fluoride 
would  be  volatilized  in  the  evaporation  with  hydrochloric 
acid  for  the  separation  of  the  silica. 

Fluorine.  One  gram  sample  is  very  finelv  around, 
slowly  fused  with  two  grams  each  of  potassium  carbonate 


1  Compte  Rendus  8,  p.  48®. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


3 


and  sodium  carbonate.  The  melt  should  be  kept  in  quiet 
fusion  over  as  low  a  flame  as  possible  for  one  hour.  The 
melt  is  transferred,  (after  cooling  quickly  by  giving  the 
crucible  a  gyratory  motion  while  held  in  the  tongs,  causing 
the  melt  to  cling  to  the  sides  instead  of  forming  a  solid 
cake  in  the  bottom),  to  a  platinum  dish  where  it  is  covered 
with  a  watch  glass  and  boiled  vigorously  with  one  hundred 
cc.  of  water.  The  residue  is  filtered  oft  and  is  saved  for 
the  determination  of  the  metallic  oxides  and  the  silica. 

The  covered  solution  is  digested  on  a  steam  bath  for 
an  hour  with  several  grams  of  ammonium  carbonate,  and 
on  cooling  more  carbonate  is  added  and  the  solution  is 
allowed  to  stand  for  twelve  hours.  The  precipitate  of 
silica,  alumina,  etc.,  is  filtered  oft,  washed  with  ammonium 
carbonate  water  and  is  saved  for  further  determinations. 

The  solution  containing  all  the  fluorine  and  traces  of 
silica,  phosphate,  etc.,  is  evaporated  until  gummy, 
then  diluted  with  water  and  neutralized  as  follows : 
Phenolplithalein  is  added,  and  nitric  acid  (double  nor¬ 
mal)  drop  by  drop  until  solution  is  colorless. 

The  solution  is  boiled  and  the  red  color  which  reap¬ 
pears  is  again  discharged  with  nitric  acid,  boiled  again 
and  neutralized  again  until  one  cc.  of  acid  will  discharge 
the  color. 

The  last  traces  of  silica,  etc.,  are  now  removed,  as 
recommended  by  F.  Seemann  (Zeit.  Anal.  Chem.  44,  p. 
343),  by  the  addition  of  20  cc.  of  Schaffgotsch  solution. 
This  solution  is  made  as  follows :  250  grams  of  ammonium 
carbonate  are  dissolved  in  180  cc.  of  ammonia  (0.92  sp.  gr.) 
and  the  solution  is  made  up  to  one  liter.  To  the  cold  solu¬ 
tion  20  grams  of  freshly  precipitated  mercuric  oxide  are 
added  and  the  solution  is  vigorously  shaken  until  the  mer¬ 
curic  oxide  is  dissolved. 

The  precipitate  caused  by  the  Schaffgotsch  solution 
is  filtered  off  and  saved,  and  the  solution  is  evaporated  to 
dryness  and  the  residue  taken  up  with  water. 

Any  phosphorus  from  the  bone  ash  used  in  some  enam- 


4  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

els,  and  chromium  which  may  be  present,  are  removed 
from  this  alkaline  solution  by  adding  silver  nitrate  in  ex¬ 
cess.  Phosphate,  chromate  and  carbonate  of  silver  are 
here  thrown  down  and  may  be  determined  if  desired. 

The  excess  of  silver  is  removed  from  the  solution  by 
sodium  chloride,  and  one  cc.  double  normal  sodium  carbo¬ 
nate  solution  is  added  to  the  filtrate,  and  the  fluorine  is 
precipitated  by  boiling  with  a  large  excess  of  calcium- 
chloride  solution. 

The  precipitate,  consisting  of  a  mixture  of  calcium 
carbonate  and  fluoT*\de,  is  collected  on  a  blue  ribbon  filter 
paper  and  is  washed,  dried,  ignited  at  low  red  heat,  sep¬ 
arated  from  the  filter  paper,  and  the  residue  with  the  ash 
of  the  paper  is  treated  with  dilute  acetic  acid  until  carbon 
dioxide  is  no  longer  given  off  on  heating.  The  liquid  is 
then  evaporated  to  dryness,  the  residue  taken  up  with  hot 
water  (slightly  acidified  with  acetic  acid)  filtered,  dried 
and  gently  ignited  and  weighed  as  CaF2.  This  may  be 
checked  by  heating  with  sulfuric  acid,  driving  off  all  the 
excess  of  acid  and  reweighing  as  OaSOt.  This  method  gives 
results  for  the  amount  of  fluorine  checking  within  0.2%, 
but  which  are  generally  from  2%  to  4%  low. 

Silica.  For  the  estimation  of  silica  and  the  metallic 
oxides,  first  the  precipitate  from  the  Sehaffgotsch  mercuric 
oxide  solution  is  ignited  to  drive  off  the  mercuric  oxide, 
and  the  silica  left  is  weighed.  The  residue  from  the  origi¬ 
nal  melt,  together  with  the  precipitate  obtained  by  ammon¬ 
ium  carbonate  (after  the  drying  and  removal  from  the 
filter  paper  whose  ash  is  added)  are  then  dissolved  in 
hydrochloric  acid.  The  solution  is  evaporated  to  dryness 
and  moistened  with  hydrochloric  acid.  It  is  diluted  with 
water  and  the  silica  is  filtered  off,  weighed,  and  this  with 
that  previously  obtained  is  the  total  silica. 

Iron ,  Alumina  and  Manganese.  The  solution  from 
the  silica  is  raised  to  boiling  and  the  iron  and  aluminum 
are  precipitated  as  hydroxides.  Then  5  cc.  of  bromine 
water  is  added  and  the  boiling  continued  for  five  minutes. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


o 


The  precipitate  is  dried  on  filter  paper  and  ignited  separ¬ 
ately  from  it  in  a  weighed  platinum  crucible,  to  which  the 
ash  of  the  filter-paper  is  afterwards  added.  The  precipi¬ 
tate  consists  of  A1203,  Fe203,  and  Mn203,  and  is 
weighed  as  such.  It  is  then  fused  with  fifteen  times  its 
weight  of  potassium  pyrosulfate  over  a  low  flame  for  three 
hours  with  the  crucible  covered.  The  crucible,  contents 
and  cover  are  placed  in  a  beaker  and  dilute  sulfuric  acid 
( 10 :1 )  is  added.  By  warming  and  continued  shaking  of 
liquid  complete  solution  may  be  obtained.  It  is  then 
drawn  through  a  Jones  lieductor  to  change  all  the  iron 
to  ferrous  and  titrated  with  N /10  potassium  permanganate 
solution.  The  iron  is  calculated  to  Fe203  and  the  alumina 
determined  by  difference. 

If  manganese  is  present  it  is  determined  in  a  separate 
sample  in  a  method  given  later  and  is  subtracted  from  the 
iron  in  the  above.  In  white  enamels  containing  only  a 
trace  of  iron  the  manganese  may  be  determined  in  the  solu¬ 
tion  from  the  pyrosulfate  fusion.  A  freshly  prepared 
solution  of  potassium  ferricyanide  is  added  to  oxidize  the 
manganese,  then  the  solution  is  made  alkaline  with  sodium 
hydroxide  solution  and  the  manganese-dioxide  thus  formed 
is  filtered  off.  The  solution  is  then  made  acid  and  the 
ferrocyanide  is  titrated  with  N/10  potassium  permanga¬ 
nate  solution.  (1  cc.  KMn04  =  0.00435  gram  MnO.) 

Calcium  Oxide.  The  filtrate  from  the  iron  and 
alumina  is  raised  to  boiling,  treated  with  boiling  ammon¬ 
ium  oxalate  solution  and  digested  on  water  bath  until 
precipitate  readily  and  quickly  settles  after  being  stirred. 
The  calcium  oxalate  is  now  filtered  off  and  ignited  wet  in 
platinum  to  constant  weight  over  a  strong  blast. 

Magnesium  Oxide.  The  solution  is  evaporated  to 
dryness  and  the  residue  ignited  to  remove  ammonium  salts. 
The  residue  is  treated  with  a  few  drops  of  hydrochloric 
acid  and  taken  up  with  boiling  water  and  filtered  from 
the  carbonaceous  residue.  To  the  boiling  solution  is  added 
drop  by  drop  a  solution  of  sodium  ammonium  phosphate 


6  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

and  is  allowed  to  cool.  Half  as  much  concentrated  am¬ 
monium  hydroxide  is  added  as  there  is  solution  and  it  is 
allowed  to  stand  over  night.  The  precipitate  is  collected 
on  a  filter,  washed  with  3%  ammonia  water,  dried  in  oven 
and  ignited  separate  from  the  filter.  The  heat  is  applied 
gently  at  first  and  finally  with  the  highest  heat  of  a  good 
Bunsen  burner.  It  is  then  weighed  as  Mg2P207. 

1  gram  Mg2P207  =  .3625  grams  MgO. 

The  alkalies  are  determined  by  the  method  of  J.  Law¬ 
rence  Smith  from  a  gram  sample  finely  powdered.  This 
method  is  standard  and  need  not  be  given  here. 

Separation  and  Determination  of  Antimony,  Tin. 

Manganese  and  Cobalt  in  Enamel. 

Decomposition .  Two  grams  finely  powdered  sample 
are  transferred  to  a  platinum  dish,  and  after  moistening 
with  a  little  water,  pure  hydrofluoric  acid  is  added  and 
the  Avhole  is  mixed  with  a  platinum  spatula.  The  dish  is 
digested  on  steam  bath  for  five  hours  covered  with  plati¬ 
num  cover  (a  larger  platinum  dish  may  be  used  for  cover 
if  no  other  is  at  hand).  After  the  decomposition  is  com¬ 
plete  the  solution  is  evaporated  to  dryness  on  steam  bath. 
The  residue  is  moistened  with  enough  dilute  sulfuric  acid 
(1:1)  to  make  a  thin  paste,  and  evaporated  as  far  as 
possible  on  a  steam  bath  and  then  on  a  hot  plate,  all  the 
time  being  covered  to  prevent  spirting.  As  soon  as  fumes 
of  sulfuric  anhydride  cease  to  be  evolved  the  cover  is 
strongly  heated  until  fumes  cease  to  be  driven  off,  when  it 
is  removed.  The  contents  are  heated  by  bringing 
the  dish  to  dull  redness  directly  over  a  Bunsen  burner. 
The  sulfates  thus  formed  are  moistened  with  strong  hydro¬ 
chloric  acid,  a  little  hot  water  is  added  and  the  solution 
boiled  with  repeated  additions  of  acid  and  water  until 
completely  in  solution.  In  some  enamels — especially  those 
with  high  melting  points — the  stannic  oxide  remains  un- 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


7 


dissolved,  and  a  fusion  of  the  residue  with  sulfur  and 
sodium  carbonate  as  given  later  under  “The  Analysis  of 
Oxide  of  Tin”  may  be  necessary. 

Treatment  with  H28.  The  solution  containing  at 
least  30  cc.  double  normal  hydrochloric  acid  is  transferred 
to  a  500  cc.  Ebrlenmeyer  flask  fitted  with  a  double  bored 
stopper.  Through  one  of  the  holes  a  right-angled  piece  of 
glass  tubing  is  introduced  that  just  reaches  to  the  lower 
edge  of  the  stopper,  while  through  another  hole  another 
right-angled  glass  tube  is  fixed  so  that  it  almost  reaches 
the  bottom  of  the  flask. 

A  Kipp  H2S  generator  is  connected  to  the  longer  tube 
and  H2S  is  passed  through  for  half  an  hour  and  the  solu¬ 
tion  is  let  stand  for  another  half  an  hour,  after  which  the 
sulfides  of  antimony  and  tin  are  transferred  to  a  filter 
paper  and  the  solution  is  kept  for  the  determination  of 
manganese  and  cobalt. 

Antimony  and  Tin.  The  precipitated  sulfides  are 
dissolved  in  a  solution  of  potassium  polysulfide — if  any 
lead  or  copper  is  present  it  will  remain  undissolved  and 
may  be  determined  separately — by  pouring  this  succes¬ 
sively  through  the  filter  into  a  300  cc.  Jena  beaker,  and 
finally  washing  with  water  containing  a  small  amount  of 
potassium  poly  sulfide. 

Antimony.  The  antimony  and  tin  in  this  solution 
are  separated  by  F.  W.  Clark’s  method  as  modified  by  F. 
Henz1,  as  follows : 

To  the  solution  in  the  Jena  beaker  6  grams  caustic 
potash  and  3  grams  tartaric  acid  are  added.  To  this 
mixture  twice  as  much  30  per  cent,  hydrogen  peroxide  is 
added  as  is  necessary  to  completely  decolorize  the  solution, 
and  the  latter  is  now  heated  to  boiling  and  kept  there  until 
the  evolution  of  oxygen  is  over,  in  order  to  oxidize  the 
thiosulphate  formed.  All  of  the  excess  of  peroxide  cannot 
be  removed  successfully  at  this  point.  The  solution  is 
cooled  somewhat,  the  beaker  covered  with  a  watch-glass, 


1  Treadwell,  Vol.  II,  p.  188. 


8  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

and  a  liot  solution  of  15  grams  pure  recrystallized  oxalic 
acid  is  cautiously  added  (5  gms.  for  0.1  grn.  of  the  mixed 
metals).  This  causes  the  evolution  of  considerable  carbon 
dioxide.  Now,  in  order  to  completely  remove  the  excess 
of  hydrogen  peroxide  the  solution  is  boiled  vigorously  for 
ten  minutes.  The  volume  of  the  liquid  should  amount  to 
from  80  to  100  cc.  After  this  a  rapid  stream  of  hydrogen 
sulfide  is  conducted  into  the  boiling  solution,  and  for 
some  time  there  will  be  no  precipitation,  but  only  a  white 
turbidity  formed.  At  the  end  of  five  or  ten  minutes  the 
solution  becomes  orange  colored  and  the  antimony  begins 
to  precipitate,  and  from  this  point  the  time  is  taken.  At 
the  end  of  fifteen  minutes  the  solution  is  diluted  with  hot 
water  to  a  volume  of  250  cc.,  at  the  end  of  another  fifteen 
minutes  the  flame  is  removed,  and  ten  minutes  later  the 
current  of  hydrogen  sulfide  is  stopped.  The  precipitated 
antimony  pentasulfide  is  filtered  off  through  a  Gooch 
crucible  which,  before  weighing  and  after  drying,  has  been 
heated  in  a  stream  of  carbon  dioxide  at  300°  O.  for  at  least 
one  hour.  The  precipitate  is  washed  twice  by  decantation 
with  1  per  cent,  oxalic  acid  and  twice  with  very  dilute 
acetic  acid  before  bringing  it  in  the  crucible.  Both  of 
these  wash  liquids  should  be  boiling  hot  and  saturated 
with  hydrogen  sulfide. 

The  crucible  is  heated  in  a  current  of  carbon  dioxide 
(free  from  air)  to  constant  weight,  and  its  contents 
weighed  as  Sb2S3. 

The  filtrate  is  evaporated  to  a  volume  of  about  225 
cc.,  transferred  to  a  weighed  unpolished  platinum  dish,  and 
electrolyzed  at  60°  to  80° C.  with  a  current  of  0.2  to  0.3 
ampere  (corresponding  to  2  to  3  volts).  For  very  small 
amounts  of  tin,  a  current  of  not  over  0.2  ampere  should  be 
used.  At  the  end  of  six  hours  8  cc.  of  sulfuric  acid  (1:1) 
are  added,  and  at  the  end  of  twenty-four  hours  the  solu¬ 
tion  is  transferred  to  another  dish.  The  deposited  tin  has 
a  beautiful  appearance,  similar  to  silver. 

Tin.  The  plated  tin  is  washed  thoroughly  with  water 
and  the  dish  is  dried  in  an  air  oven  at  110°  and  weighed. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


9 


The  solution  containing  the  cobalt  and  manganese  is 
boiled  until  free  from  H2S.  The  iron  is  oxidized  back  to 
the  ferric  state  by  the  addition  of  bromine  water  and 
boiling  until  the  excess  of  the  latter  is  expelled.  Ten  cc. 
double  normal  ammonium  chloride  is  added  and  the  iron 
and  alumina  are  precipitated  by  the  addition  of  ammonia 
and  are  filtered  off.  ( The  iron  alumina  may  be  determined 
from  this  precipitate  if  desired.) 

The  solution  still  containing  the  manganese  and  co¬ 
balt  is  transferred  to  an  Ehrlenmeyer  flask  fitted  for  pass¬ 
ing  in  H2S,  as  before  described,  and  3  cc.  strong  ammonia 
is  added.  H2S  is  passed  through  for  some  time,  and  after 
precipitation  ceases  3  cc.  more  of  ammonia  are  added  and 
the  flask  is  filled  to  the  neck  (300  cc.  flask),  is  corked  and 
set  aside  for  twelve  hours  at  least.  The  precipitate  is 
collected  and  washed  on  a  small  filter  with  water  contain¬ 
ing  amonium  chloride  and  sulfide. 

Manganese.  The  manganese  is  extracted  from  the 
precipitate  on  the  filter  by  pouring  through  it  strong  H2S 
water  acidified  with  %  its  volume  hydrochloric  acid  (sp. 
gr.  1.11).  This  solution  from  the  extraction  is  evaporated 
to  dryness,  ammonium  salts  are  destroyed  by  evaporation 
with  a  few  drop  of  sodium  carbonate  solution,  hydro¬ 
chloric  add  and  a  drop  of  sulfurous  acid  are  added  to 
decompose  excess  of  carbonate  and  to  dissolve  the  pre¬ 
cipitated  manganese,  and  the  latter  is  reprecipitated  at 
boiling  heat  by  sodium  carbonate  after  evaporating  off  the 
hydrochloric  acid.  The  manganese  is  weighed  as  Mn304 
and  calculated  to  Mn02,  in  which  form  it  is  probably 
present  in  the  enamel. 

The  residue  of  cobalt  sulfide  left  after  extracting  the 
manganese  is  burned  in  a  porcelain  crucible,  dissolved  in 
aqua  regia,  and  evaporated  with  hydrochloric  acid;  the 
platinum — and  copper  if  any  is  present — are  thrown  down 
by  heating  and  passing  in  hydrogen  sulfide.  The  filtrate 
from  the  platinum  and  copper  is  made  ammoniacal,  and 
cobalt  is  thrown  down  by  hydrogen  sulfide.  This  is  filtered 


lo  ANALYSIS  FOB  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

oft*  and  washed  with  water  containing  ammonium  sulfide. 
This  is  either  ignited  and  weighed  as  oxide  or  more  accur¬ 
ately  determined  by  dissolving  in  an  ammoniacal  solution 
of  ammonium  sulfate,  containing  10  grams  of  ammonium 
sulfate  and  40  cc.  of  concentrated  ammonia  for  each  0.3 
grains  of  cobalt,  and  electrolyzing  in  a  weighed  platinum 
dish  at  room  temperature  with  a  current  of  0.5  to  1.5 
ampere,  and  an  electromotive  force  of  2.8  to  3.3  volts.  The, 
electrolysis  is  finished  in  three  hours.  The  circuit  is 
broken  and  the  liquid  poured  off,  and  the  platinum  dish  is 
washed  with  water,  then  with  absolute  alcohol  (distilled 
one  hour)  and  finally  with  ether,  allowed  to  dry  in  oven 
at  95°  for  one  minute  and  then  weighed.  The  metallic 
cobalt  is  calculated  as  CoO,  in  which  form  it  is  present  in 
the  enamel. 

The  Determination  of  Boric  Anhydride  in  Enamel. 

The  boron  is  determined  in  a  separate  sample  of  about 
0.3  grams.  This  finely  pulverized  sample  is  fused  with 
three  grams  sodium  carbonate  for  fifteen  minutes,  is  taken 
up  with  thirty  cc.  dilute  hydrochloric  acid  and  a  few  drops 
of  nitric  acid.  The  melt  is  heated  in  a  250  cc.  round-bot¬ 
tomed  flask  almost  to  boiling,  and  dry  precipitated  cal¬ 
cium  carbonate  is  added  in  moderate  excess.  The  solution 
is  boiled  in  the  flask  after  it  has  been  connected  with  a 
six-inch  worm  reflux  condenser.  The  precipitate  is  filtered 
on  an  8  cm.  Buchner1  funnel,  and  is  Avashed  several  times 
with  hot  Avater,  taking  care  that  the  total  volume  of  the 
liquid  does  not  exceed  100  cc. 

The  filtrate  is  returned  to  the  flask,  a  pinch  of  calcium 
carbonate  is  added  and  the  solution  is  heated  to  boiling  to 
remove  the  free  carbon  dioxide.  This  is  best  done  by  con¬ 
necting  the  flask  to  a  suction  pump,  and  the  suction  is  ap¬ 
plied  during  boiling.  The  solution  is  cooled  to  ordinary 


1  See  Method  of  Wherry  and  Chapin,  Jr..  Am.  Chem.  Soc.  30.  p.  168$.  for 
Determination  of  Boron  in  Silicates. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


11 


temperature,  filtered  if  the  precipitate  has  a  red  color,  and 
four  or  five  drops  of  phenolphthalein  is  added  and  N/10 
sodium  hydroxide  solution  is  run  in  slowly  until  liquid 
has  a  strongly  pink  color.  A  gram  of  mannite  (or  150  cc. 
of  neutral  glycerol)  is  added,  whereupon  the  pink  color 
will  disappear.  Continue  to  run  in  N/10  sodium  hydroxide 
until  end  point  is  reached.  Add  more  mannite  or  glycerol 
and  if  necessary  more  alkali,  until  a  permanent  pink  color 
is  obtained. 

1  cc.  N/10  Sodium  Hydroxide  =  .0035  g.  B203. 


Lead.  The  enamel  for  cooking  utensils  should  never 
contain  lead.  To  determine  whether  a  cooking  utensil 
contains  lead,  E.  Adam  gives  the  following  simple  qualita¬ 
tive  method :  A  small  piece  of  filter  paper  moistened  with 
hydrofluoric  acid  is  placed  upon  the  enamel  and  allowed 
to  remain  for  some  minutes;  the  paper,  together  with  any 
pasty  mass  adhering  to  the  enamel,  is  then  washed  off  into 
a  small  platinum  basin,  diluted  with  water,  and  tested 
for  lead  by  passing  H2S  through  the  solution. 

J.  Grunwald  (Oesterr.  Chem.  Ztg.  8,  p.  46)  gives  an¬ 
other  quick  test  for  lead  :  Wet  small  portion  of  surface  with 
HN03  (cone.)  and  heat  until  acid  is  evaporated.  Add 
several  drops  of  water  and  a  few  drops  10%  potassium 
iodide  solution,  and  if  even  a  trace  of  lead  is  present  yel¬ 
low  lead-iodide  will  be  produced. 

Determination  of  Phosphoric  Anhydride  in  Enamel. 

Enamels  containing  bone  ash  to  give  opaqueness  are 
analyzed  for  P205  as  follows: 

To  a  gram  sample  of  very  finely  pulverized  enamel  in 
a  platinum  crucible  one  cc.  of  sulfuric  acid  is  added  and 
the  crucible  is  filled  half  full  (about  ten  cc.  are  required) 
with  hydrofluoric  acid.  The  crucible  is  heated  on  the 
water  bath  until  most  of  the  solution  is  evaporated  and 
then  gently  on  a  hot  plate  to  remove  all  the  fluorine  as 


12  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

silicon-tetra-fiuoride  and  as  hydrofluoric  acid,  but  no 
sulfuric  acid  fumes  should  evolve,  as  P205  is  volatile.  The 
residue  is  dissolved  in  nitric  acid  and  taken  to  dryness, 
moistened  with  nitric  acid,  diluted  with  water,  filtered 
and  washed  with  a  very  little  water. 

Add  aqueous  ammonia  to  the  solution  from  above 
until  the  precipitate  of  calcium  phosphate  first  produced 
just  fails  to  redissolve,  and  then  dissolve  this  by  adding  a 
few  drops  of  nitric  acid.  Warm  the  solution  to  about 
70 °C.  and  add  50  cc.  ammonium  molybdate  solution  (70g. 
Mo03  per  liter).  Allow  the  mixture  to  digest  at  50°  for 
twelve  hours.  Filter  off  precipitate  washing  by  decanta¬ 
tion  with  a  solution  of  ammonium  nitrate  made  acid  with 
nitric  acid. 

The  precipitate  on  the  filter  is  dissolved  by  pouring 
through  it  dilute  ammonia  solution  (one  volume  of  0.90 
sp.  gr.  ammonia  to  three  volumes  of  water). 

The  solution  is  received  in  the  beaker  containing  the 
bulk  of  the  precipitate,  all  of  which  is  dissolved  in  the 
ammonia  solution. 

An  excess  of  magnesium  ammonium  chloride  (“mag¬ 
nesia  mixture”)  solution  is  added  very  slowly  and  with 
constant  stirring.  Let  solution  stand  over  night.  Decant 
clear  solution  through  a  filter  and  wash  by  decantation 
with  ammonia  water  (1:3).  Dissolve  the  precipitate  by 
pouring  a  little  hydrochloric  acid  (sp.  gr.  1.12)  through 
the  filter,  allowing  the  acid  solution  to  run  into  the  beaker 
containing  most  of  the  precipitate.  When  all  the  precipi¬ 
tate  on  the  filter  and  in  the  beaker  is  dissolved  wash  the 
filter  paper  with  a  little  hot  water.  To  the  solution  add 
2  cc.  magnesia  mixture  and  then  strong  ammonia,  drop  by 
drop,  with  constant  stirring  until  distinctly  ammoniacal. 
Stir  several  minutes  then  add  strong  ammonia  equal  to 
one-third  of  the  liquid,  let  stand  two  hours  and  filter  off 
the  precipitate  of  magnesium  ammonium  phosphate.  Wash 
with  dilute  ammonia  water,  dry  the  precipitate,  ignite 
separately  from  the  filter,  first  at  low  temperature  and 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS.  13 


gradually  raise  to  full  blast.  Weigh  precipitate  as 
Mg2P207  and  calculate  as  P205  in  sample. 

PART  II. 

THE  ANALYSIS  OF  ENAMEL  RAW  MATERIALS. 

The  Analysis  of  Borax. 

Sampling.  A  handful  is  taken  from  the  middle  of 
every  tenth  bag  as  it  is  unloaded.  The  sample  from  the 
entire  car-load  is  then  quartered  down  to  two  pounds. 
This  is  crushed  so  that  it  Avill  pass  through  a  forty  mesh 
sieve.  This  is  further  quartered  to  about  thirty  grams. 
Sample  is  then  accurately  weighed  and  thoroughly  dis¬ 
solved  in  about  600  cc.  hot — not  boiling — water  in  a  liter 
volumetric  flask,  and  when  cool  is  diluted  to  the  mark. 
One  hundred  cc.  of  this,  representing  one-tenth  of  the 
sample,  is  then  taken  for  analysis. 

Determination  of  Sodium  Oxide  and  Jtoric  Acid. 
Titrate  with  normal  sulfuric  or  hydrochloric  acid  solution, 
using  methyl  orange  as  indicator. 

Number  cubic  centimeters  Normal  Acid  X  .031  =  g, 
Na20.  The  solution  is  now  boiled,  covered  with  a 
watch  glass  to  expel  C02,  and  on  cooling  may  turn  pink. 
Add  normal  KOH  solution  (a  drop  will  do)  to  bring  back 
yellow  color.  At  this  stage  all  the  boric  acid  exists  in  a 
free  state. 

(2Na+-f-B40”)  +H20+  (2H+4-2C1-)— (2Na++2Cl-)  +4(H++4B02-) 

Add  as  much  neutral  glycerol  as  there  is  solution 
(about  150  cc.)  and  titrate  with  normal  potassium  hy¬ 
droxide,  using  phenolphthalein  as  indicator.  If  end  is 
not  distinct  add  more  glycerol  and  more  indicator..  The 
addition  of  glycerol  causes  the  boric  acid  to  become  more 
dissociated,  probably  due  to  the  formation  of  boroglv ceric 
acid,  and  the  end-point  is  quite  distinct.  The  following 
equation  represents  essentially  what  takes  place: 

(4H++4B02-)  +  (4K++40H-)  =  (4K++4BOr) +4H20. 

1  cc.  normal  KOH  solution  =  .035  g.  B203. 


14  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

If  the  analysis  gives  more  Na20  than  is  required  to 
calculate  all  the  B203  to  Na2B407,  the  remainder  comes 
from  sodium  carbonate  with  which  it  lias  been  adulterated. 

Calculation  of  Results.  The  analysis  of  the  borax 
is  very  important,  as  many  times  samples  are  adulterated, 
and  even  when  not  adulterated  seldom  contain  exactly 
enough  water  to  give  the  formula  Na2B407  •  10H2O.  It  is 
necessary  to  know  the  strength  of  the  borax  not  only  to 
buy  intelligently,  but  also  so  that  each  and  every  mix  of 
enamel  will  contain  the  same  amount  of  borax. 

It  is  customary  to  calculate  from  the  percent  of  B203 
in  sample  the  percent  strength  of  the  sample  as  Na9  *  B4Ov  • 

ioh2o. 

%B2O3X2.7307  =  %Na2B4O7  •  10H2O. 

When  the  sample  has  dehydrated  of  course  this  will 
run  over  100%,  and  thus  the  correspondingly  fewer  pounds 
of  borax  may  be  used  in  the  mix  of  enamel. 

Moisture.  On  account  of  the- large  amount  of  water 
of  crystallization  in  borax  it  is  difficult  to  determine  the 
moisture  directly,  therefore  it  is  calculated  by  subtracting 
the  %  Na2B407  •  10H2O  and  the  %  Na2C03  (if  any  is 
present)  from  100%. 

The  Analysis  of  Ground  Sand,  Flint  and  Quartz. 

Fineness.  These,  as  are  most  of  the  raw  materials 
used  in  the  enamel,  are  tested  for  fineness.  One  kilogram 
is  weighed  on  balance  sensitive  to  1/10  gram  and  is  shaken 
on  a  100  mesh  sieve.  The  material  remaining  on  the  sieve 
is  weighed.  This  is  then  shaken  on  an  80  mesh  sieve  and 
the  residue  weighed.  From  this  is  calculated  percent 
through  100  mesh  and  percent  through  80  mesh.  The  finer 
the  material  the  better  it  is  for  use  in  making  enamel. 

An  analysis  for  SiO?,  Fe203  and  MgO  is  run  when  a 
new  material  is  being  tried,  but  generally  only  the  Si02 
and  Fe203  are  determined.  In  this  case  the  acid  solution 
from  the  silica  is  reduced  by  passing  through  a  Jones 
Reductor  and  is  titrated  with  N/10  potassium  bichromate. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS.  lf> 

Preparation  for  Analysis.  The  material  is  carefully 
sampled  by  quartering  down  to  several  grams.  This  is 
ground  in  an  agate  mortar  to  pass  completely  through  a 
hundred  mesh  sieve.  This  grinding  is  generally  done  by 
hand  but  an  enameling  works  laboratory  should  be  equip¬ 
ped  with  a  McKenna  Grinder,  (manufactured  by  McKenna 
Bros.  Brass  Company,  Ltd.,  of  Pittsburgh),  in  which  the 
material  can  be  ground  in  an  agate  mortar  by  power. 

The  method  followed  for  the  analysis  of  flint  and 
other  forms  of  silica  as  well  as  clays  and  feldspars,  is  in 
all  essentials,  a  well  known  method  given  by  Hillebrand  in 
analysis  of  silicate  rocks,  U.  S.  Geological  Survey  Bull. 
305,  and  for  reasons  of  space  this  method  will  not  be  given 
here. 

The  Determination  of  Titanium  in  Enamels,  Clays  and 
Silicate  Minerals. 

Titanium  is  determined  after  the  determination  of  the 
iron  by  titrating  with  permanganate.  This  solution  (after 
titrating)  is  diluted  to  1000  cc.  and  is  treated  with  hydro¬ 
gen  peroxide  and  the  titanium  determined  by  A.  Weller’s 
Colorimetric  Method,1  from  one-half  the  solution. 

This  determination  depends  upon  the  fact  that  acid 
solutions  of  titanium  sulphate  are  colored  intensely  yel¬ 
low  when  treated  with  hydrogen  peroxide;  the  yellow  color 
increases  with  the  amount  of  titanium  present  and  is  not 
altered  by  an  excess  of  hydrogen  peroxide.  On  the  other 
hand,  inaccurate  results  are  obtained  in  the  presence  of 
hydro-fluoric  acid  (Hillebrand)  ;  consequently  it  is  not 
permissible  to  use  hydrogen  peroxide  for  this  determina¬ 
tion  which  has  been  prepared  from  barium  peroxide  by 
means  of  hydrofluosilicic  acid.  Furthermore,  chromic, 
vanadic,  and  molybdic  acids  must  not  be  present,  since 
they  also  give  colorations  with  hydrogen  peroxide.  The 
presence  of  small  amounts  of  iron  do  not  affect  the  reac- 


2  Berichte  15,  p.  25-93. 


16  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERLVLS. 


tion,  but  large  amounts  of  iron  cause  trouble  on  account 
of  the  color  of  the  iron  solution.  If,  however,  phosphoric 
acid  is  added  to  the  colored  ferric  solution  it  becomes  de¬ 
colorized,  and  from  such  a  solution  the  determination  of 
titanium  offers  no  difficulty.  The.  solution  in  which  the 
titanium  is  to  be  determined  must  contain  at  least  5  per 
cent,  of  sulfuric  acid;  an  excess  does  not  influence  the 
reaction.  The  reaction  is  so  delicate  that  0.00005  gm.  of 
Ti02  present  as  sulphate  in  50  cc.  of  solution  give  a  dis¬ 
tinctly  visible  yellow  coloration. 

For  this  determination  a  standard  solution  of  titan¬ 
ium  sulfate  is  required.  This  can  be  prepared  by  taking 
0.6000  gm.  of  potassium  titanic  fluoride  which  has  been 
several  times  recrystallized  and  gently  ignited  (corres¬ 
ponding  to  0.2  gm.  of  Ti02).  This  is  treated  in  a  platinum 
crucible  several  times  with  a  little  water  and  concentrated 
sulfuric  acid,  expelling  the  excess  of  acid  by  gentle  igni¬ 
tion,  finally  dissolving  in  a  little  concentrated  sulfuric 
acid  and  diluting  with  5  per  cent,  sulfuric  acid  to  100  cc. 
One  cubic  centimeter  of  this  solution  corresponds  to  0.002 
gm.  Ti02. 

The  determination  proper  is  carried  out  in  the  same 
way  as  the  colorimetric  determination  of  ammonium  in 
the  sanitary  analysis  of  water. 

50  cc.  of  the  solution  which  has  been  brought  to  a 
definite  and  accurately  measured  volume  is  placed  in  a 
Nessler  tube  beside  a  series  of  other  tubes,  each  containing 
a  known  amount  of  the  standard  titanium  solution,  filled 
up  to  the  mark  with  water  and  each  treated  with  2  cc.  of  3 
per  cent,  hydrogen  peroxide1  (free  from  hydrofluoric 
acid).  The  color  of  the  solution  in  question  is  compared 
with  the  standards.  This  method  is  only  suitable  for  the 
estimation  of  small  amounts  of  titanium,  as  the  shades 
of  strongly  colored  solutions  cannot  be  compared  accur¬ 
ately. 


1  The  hydrogen  peroxide  solution  is  prepared  shortly  before  using  by 
dissolving  commercial  potassium  percarbonate  in  dilute  sulfuric  acid. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


17 


The  Analysis  of  Oxide  of  Tin. 

Stannic  Oxide.  As  this  is  one  of  the  most  important 
and  most  expensive  of  the  raw  materials  used  in  enamel¬ 
ing,  an  analysis  is  very  necessary.  The  oxide  is  bought  to 
contain  not  less  than  99.5%  Sn02,  and  in  this  the  impuri¬ 
ties  will  consist  of  minute  traces  only  of  other  materials. 
For  an  oxide  of  this  kind  from  .2  to  .3  of  a  gram  of  the 
sample  is  placed  in  a  porcelain  casserole,  about  10  cc.  of 
C.  P.  nitric  acid  of  a  sp.  gr.  1.2  is  added  and  the  solution 
is  slowly  evaporated  to  a  volume  of  about  2  or  3  cc.,  diluted 
to  about  30  or  40  cc.  of  water,  kept  warm  for  about  a  half 
hour,  filtered  on  a  small  blue-ribbon  filter  paper,  and 
washed  with  warm  water,  slightly  acidulated  with  nitric 
acid,  being  careful  to  avoid  letting  the  precipitate  creep 
up. 

The  precipitate  is  dried  on  filter  paper  in  the  funnel 
by  placing  in  a  hot  air  bath.  The  dried  tin  oxide  is  then 
removed  as  completely  as  possible  from  the  filter  paper  and 
the  paper  is  ignited  in  a  porcelain  crucible,  being  sure  that 
there  is  an  excess  of  air  so  that  there  will  be  no  metallic 
tin  reduced. 

The  balance  of  oxide  of  tin  is  now  added  to  the  cru¬ 
cible  and  the  whole  is  moistened  with  a  drop  of  nitric  acid, 
the  temperature  under  the  crucible  is  gradually  raised 
until  it  comes  to  a  bright  red  heat  over  the  blast  flame. 

This  method  gives  results  which  check  within  one- 
tenth  of  a  per  cent. 

Some  brands  of  oxide  of  tin  on  the  market  contain  a 
number  of  impurities  in  considerable  quantities.  Lead, 
iron,  silica,  sodium  chloride,  sodium  sulfate  and  water 
are  the  most  common  of  these.  These  are  determined  as 
follows : 

Direct  Method.  Methods  for  the  direct  determination 
of  the  tin  have  proven  quite  unsatisfactory  but  the  follow¬ 
ing,  with  very  careful  manipulation,  yields  results  check¬ 
ing  within  0.2%  : 

Five-tenths  grams  of  oxide  is  mixed  in  a  porcelain 
crucible  with  3  grams  each  of  powdered  sulfur  and  dry 


18  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

carbonate  of  soda,  which  both  of  course  must  be  0.  P., 
especially  free  of  metals  and  earths.  The  covered  crucible 
is  heated  for  about  an  hour  at  low  heat  first ,  and  later  at 
the  heat  of  a  regular  Bunsen  burner ;  then  let  cool  without 
lifting  the  cover.  The  cold  mass  is  dissolved  in  water, 
filtered  and  washed  with  water  to  which  was  added  a  little 
sulfide  of  ammonia;  the  residue  is  brought  back  in  the 
crucible  and  the  melting  process  repeated,  of  which  the 
solution  is  filtered  to  the  first  melting.  The  sulfide  tin 
solution  then  is  acidulated  with  hydrochloric  acid  and  the 
precipitated  sulfide  of  tin  is  allowed  to  settle  clearly,  after 
which  it  is  filtered  and  washed  with  sulfide  of  hydrogen 
water. 

The  wet  precipitate  of  sulfide  of  tin  is  transferred 
to  an  Ehrlenmeyer  flask  and  treated  with  dilute  hydro¬ 
chloric  acid  and  bromine  until  completely  dissolved,  at  a 
low  heat.  The  filter  left  after  the  solution  is  filtered  off  is 
washed  and  the  SnCl2  solution  is  precipitated  with  am¬ 
monia  and  a  little  nitrate  of  ammonia,  allowed  to  settle, 
filtered  and  washed.  After  drying,  the  precipitate  is 
ignited  at  white  heat  and  is  weighed  as  Sn02. 

Reduction  Method.  When  the  qualitative  analysis 
shows  no  metal  other  than  tin  present,  a  very  satisfactory 
method  is  to  reduce  a  weighed  quantity  of  the  sample  in  a 
Rose  crucible  by  heating  to  redness  in  a  stream  of  hydro¬ 
gen.  The  silica,  if  any  is  present,  may  be  determined  by 
dissolving  out  the  tin  with  hydrochloric  acid  and  weighing 
the  residue. 

Combined  Water.  In  oxides  which  are  prepared  by 
certain  precipitation  methods,  the  combined  water  runs  as 
high  as  ten  per  cent.  To  determine  this,  a  two  gram  sam¬ 
ple  is  heated  in  a  porcelain  crucible  at  a  white  heat  to 
constant  weight.  The  loss  is  combined  water. 

Lead.  The  lead  is  determined  from  the  nitric  acid 
solution  and  washings  from  the  tin  oxide  determination 
by  precipitation  as  the  sulfate. 

Iron.  Digest  about  one  gram  with  twenty-five  cc. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


19 


of  concentrated  hydrochloric  acid.  As  much  water  is 
added  and  the  solution  is  boiled  for  five  minutes.  The 
residue  is  filtered  off  and  about  a  cubic  centimeter  of  con¬ 
centrated  sulfuric  acid  is  added  and  the  solution  is  evap¬ 
orated  until  the  sulfuric  fumes  come  off.  The  solution  is 
diluted,  passed  through  a  Jones  Reductor  and  titrated 
with  N/10  potassium  permanganate  solution. 

Soluble  Salts.  About  two  grams  of  the  sample  is 
boiled  with  water  for  thirty  minutes.  The  residue  is  fil¬ 
tered  on  a  blue-ribbon  paper  and  is  dried  in  an  air  bath. 
It  is  then  separated  as  completely  from  the  paper  as  is 
possible.  The  paper  is  burned  in  a  platinum  crucible.  A 
drop  of  nitric  acid  is  added  and  the  crucible  is  raised  to 
bright  red.  The  whole  of  the  residue  is  now  added  and 
heated  to  white  heat  for  some  time.  (If  there  was  com¬ 
bined  water  present  in  the  sample  of  course  it  will  be 
driven  off,  and  this  must  be  taken  into  calculation ) . 

The  loss  in  weight  (minus  the  above  correction)  is 
the  soluble  salts — usually  sodium  chloride  and  sulfate. 

If  desired  these  may  be  determined  definitely  by  usual 
methods.  (Titration  of  an  aliquot  part  with  N/10  silver 
nitrate  solution  for  the  chloride  and  precipitation  of  the 
sulfate  as  barium  sulfate  in  another  aliquot  part  slightly 
acidifies  with  nitric  acid.) 

Silica,.  To  the  residue  in  the  platinum  crucible  from 
the  above  determination  several  drops  of  sulfuric  acid  are 
added,  and  the  crucible  is  filled  within  a  quarter  of  an 
inch  of  the  rim  with  pure  hydrofluoric  acid.  This  is 
volatilized,  carrying  with  it  any  of  the  silica  as  hydrofluo- 
silic  acid.  Loss  of  weight  =  Si02. 

The  Analysis  of  Pyrolusite. 

Pyrolusite  has  two  uses  in  enamel,  first  as  an  oxidiz¬ 
ing  agent,  and  second  to  give  an  amethyst  color  to  the 
enamel  frit.  Its  grading,  however,  is  generally  made  on 
its  oxidizing  value.  This  is  found  as  follows : 

Manganese  Dioxide.  A  sample  is  carefully  taken 


20  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

from  each  barrel  of  the  shipment,  and  after  quartering 
down  to  about  ten  grams  is  ground  so  as  to  pass 
through  a  200  mesh  sieve.  (It  is  better  to  test  this  by  see¬ 
ing  if  any  grit  can  be  detected  when  the  powder  is  placed 
between  the  teeth.)  The  sample  is  dried,  spread  out  on  a 
watch  glass,  at  110°  for  one  hour,  transferred  to  a  stop¬ 
pered  weighing  tube,  and  after  weighing,  about  one-half 
gram  is  transferred  into  a  250  cc.  Elirlenmeyer  flask.  For 
each  gram  of  sample  weighed  out  add  at  least  0.9  grams 
pure,  tested  oxalic  acid  (H2C204  *  2H20)  weighing  the  acid 
accurately  and  recording  the  same.  Add  about  30  cc.  of 
water  and  30  cc.  5  normal  sulfuric  acid  and  drive  off  car¬ 
bon  dioxide  by  heating  gently. 

It  is  seldom  necessary  to  filter  after  some  practice,  so 
the  solution  is  titrated  hot  for  the  excess  of  oxalic  acid 
with  N/10  potassium  permanganate  solution.  Calculate 
amount  of  oxalic  acid  oxidized  by  the  pvrolusite.  The 
reaction  is 


MnOs  +  H2C204  •  2H20  ‘j£  H2S04  =  MnS04  +  2C02  -{-  4H2Q. 


Each  gram  oxalic  acid  oxidized  therefore  corresponds 
to  .6902  g.  Mn02. 

As  pvrolusite  is  added  to  some  enamels  only  to  give 
color  it  is  sometimes  necessary  to  know  its  coloring  power, 
and  this  is  dependent  upon  the  total  manganese. 

Total  Manganese.  One-half  gram  sample  is  boiled 
with  strong  hydrochloric  acid  until  chlorine  ceases  to  be 
evolved.  The  solution  is  neutralized  with  calcium  carbon¬ 
ate  and  an  excess  of  a  strong  filtered  solution  of  bleaching 
powder  is  added.  The  solution  is  boiled  until  deep  red, 
then  alcohol  is  added  until  the  red  color  disappears.  The 
whole  of  the  manganese  now  exists  as  Mn02  and  may  be 
reduced  with  oxalic  acid  and  titrated  for  its  oxidizing 
power  as  before  with  N/10  permanganate  of  potassium. 
Each  gram  oxalic  acid  oxidized  corresponds  to  .4361  g.  Mn. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


21 


The  Analysis  of  Soda  Ash  and  Pearl  Ash. 

Generally  it  is  only  necessary  to  determine  the  total 
alkali  in  a  sample  of  either  soda  ash  or  pearl  ash,  and  to 
calculate  from  this  the  percentage  of  Na20  or  K20.  A 
more  complete  analysis  includes  the  determination  of  in¬ 
soluble  matter,  iron,  chloride,  sulfate  and  moisture,  as  well 
as  the  total  alkali. 

Insoluble  Matter.  50  g.  weighed  on  rough  balance 
(sensitive  to  0.1  g.)  and  sufficient  water  added  to  dissolve 
the  ash,  shaking  until  dissolved.  After  an  hour’s  digestion 
the  solution  is  filtered  through  a  weighed  Gooch  crucible 
with  a  circle  of  filter  paper  covering  the  bottom.  This  is 
dried  at  105°  and  the  increase  in  weight  is  insoluble 
matter. 

Iron.  The  iron  in  the  above  insoluble  matter  is  dis¬ 
solved  by  pouring  hot  dilute  hydrochloric  acid  through 
the  precipitate  in  the  Gooch  crucible.  The  iron  is  precipi¬ 
tated  from  this  by  ammonium  hydroxide  and  filtered  on  a 
white  ribbon  filter  paper.  The  still  moist  precipitate  is 
dissolved  in  sulfuric  acid,  reduced  by  means  of  a  Jones 
Reductor  and  titrated  with  N/10  permanganate. 

Chloride.  Three  gram  samples  are  dissolved  in 
water  and  nitric  acid  added  until  the  solution  is  neutral 
(test  with  litmus  paper).  It  is  then  titrated  with  N/10 
silver  nitrate  solution. 

Sulfate.  Five  or  ten  grams  are  dissolved  in  hydro¬ 
chloric  acid  and  the  sulfate  precipitated  from  the  almost 
boiling  solution  by  the  addition  of  hot  barium  chloride 
solution. 

Total  Alkali.  Twenty-five  grams  are  dissolved  in 
water  in  a  500  cc.  volumetric  flask  and  50  cc.  are  titrated 
with  N.  hydrochloric  acid,  using  methyl  orange  as  indi¬ 
cator. 

Hydroxide.  To  50  cc.  from  above,  precipitate  all  the 
carbonate  with  barium  chloride.  Without  filtering,  add 
phenolphthalein  and  titrate  until  colorless  with  normal 
hydrochloric  acid. 


22 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


Moisture.  Ten  gram  samples  are  dried  at  120°  for 
two  hours. 

The  Analysis  of  Saltpeter  and  Chili  Saltpeter. 

Moisture.  Ten  gram  samples  are  heated  to  constant 
weight  in  an  air-bath  at  130°. 

Insoluble  Matter.  Twenty  grams  are  dissolved  in 
boiling  water  and  filtered  through  a  weighed  Gooch  cru¬ 
cible  with  a  circle  of  filter  paper  on  the  bottom.  After 
drying  at  110°  in  air  bath  to  constant  weight,  the  increase 
in  weight  is  the  insoluble  matter. 

Chlorine.  The  solution  from  above — this  should  be 
about  500  cc. — is  placed  in  a  1000  cc.  volumetric  flask  and 
25  cc.  (representing  0.5  g.  sample)  is  titrated  with  N/10 
silver  nitrate,  using  potassium  chromate  as  indicator.  The 
result  is  calculated  to  sodium  chloride. 

Sulfate.  Twenty  cc.  are  heated  to  boiling  and  precip¬ 
itated  by  adding  hot  barium  chloride  solution,  a  drop  at 
a  time  and  with  constant  stirring.  After  two  hours  diges¬ 
tion  (or  until  precipitate  settles  quickly  after  agitating), 
filter  through  a  Gooch  crucible  with  ignited  asbestos  filter, 
ignite  and  weigh  as  barium  sulfate.  This  is  calculated  to 
calcium  sulfate. 

Calcium  and  Magnesium.  From  five  hundred  cc.  of 
the  above  solution  (equal  to  10  grams  sample)  at  boiling 
temperature  precipitate  the  calcium  as  oxalate  bv  the  ad¬ 
dition  of  ammonium  oxalate,  being  careful  not  to  add  much 
excess,  as  magnesium  is  to  be  determined  in  the  same 
sample.  Filter  on  a  white  ribbon  filter  paper,  after  an 
hour’s  digestion  on  the  steam  bath,  ignite  wet  paper  in 
platinum  crucible,  gradually  increase  to  full  blast  and 
heat  to  white  heat  to  constant  weight.  Weight  as  calcium 
oxide. 

Determine  the  magnesium  in  filtrate  from  the  calcium 
by  addition  of  a  solution  of  microcosmic  salt  and  after¬ 
ward  one-third  the  volume  of  concentrated  ammonium 
hydroxide,  added  drop  by  drop.  The  precipitate,  ignited 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERLYLS. 


23 


separate  from  the  filter  paper,  is  heated  at  first  gently 
and  at  last  with  the  full  heat  of  a  Bunsen  burner,  and 
weighed  as  magnesium  pyrophosphate  (Mg2P207). 

Perchlorate.  Ten  grams  of  the  sample  of  which  the 
chloride  content  lias  already  been  determined,  is  mixed 
with  an  equal  quantity  of  chemically  pure  sodium  carbon¬ 
ate,  and  is  heated  in  a  large,  covered,  platinum  crucible  to 
quiet  fusion.  Ten  or  fifteen  minutes  are  required.  The 
product  is  then  dissolved  in  nitric  acid  and  the  chloride 
estimated  as  usual. 

Nitrogen.  This  is  determined  by  the  Kjeldahl 
method  after  reducing  the  nitrate  to  ammonia.  Twenty 
grams  of  the  sample  are  ground  coarsely  and  dissolved  in 
water  in  a  liter  flask,  and  solution  is  diluted  to  the  mark. 
Twenty-five  cc.  (equal  to  0.5  g.  sample)  of  this  solution  is 
mixed  in  a  800  cc.  Kjeldahl  flask  with  15  cc.  concentrated 
sulfuric  acid  to  which  2  grams  salicylic  acid  have  been 
added,  then  add  gradually  2  grams  zinc  dust  and  shake 
flask  to  mix  contents.  Digest  over  low  flame  with  neck  of 
flask  slightly  inclined  until  danger  of  frothing  has  passed. 
Increase  flame  until  the  acid  boils  briskly  and  until  white 
fumes  cease  to  come  off.  This  usually  takes  about  ten 
minutes. 

Add  .7  gram  mercuric  oxide  and  continue  boiling, 
adding  acid  if  necessary  to  keep  solution  from  solidifying. 
Solution  should  be  clear  in  a  short  time.  Complete  oxida¬ 
tion  by  adding  a  little  powdered  potassium  permanganate 
and  allow  the  contents  to  cool.  Add  about  200  cc.  am¬ 
monia-free  water  and  25  cc.  potassium  sulfide  solution 
( 40  g.  commercial  salt  to  the  liter)  and  shake  thoroughly. 
Add  several  pieces  of  granulated  zinc  and  then  pour  care¬ 
fully  down  the  side  of  the  neck  100  cc.  sodium  hydroxide 
solution  (500  g.  per  liter),  avoiding  shaking  and  thereby 
mixing  the  acid  and  alkali.  After  washing  the  neck  with 
ammonia-free  water  connect  the  flask  immediately  with  a 
previously  set  up  block  tin  condenser,  which  has  been 
thoroughly  washed  and  the  tips  of  whose  delivery  are  irn- 


24  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 

mersed  in  30  cc.  standard  acid  solution  (half  normal), 
colored  with  methyl  orange  contained  in  a  150  cc.  Phillip’s 
flask.  Mix  contents  of  digestion  flask  by  shaking  thor¬ 
oughly,  then  heat  carefully,  then  slowly  (taking  about  an 
hour)  distill  over  200  cc.  of  the  liquid.  Titrate  excess  of 
acid  with  standard  half  normal  alkali  solution,  and  from 
this  calculate  percentage  of  nitrogen  in  sample. 

Lung  Nitrometer  M  ethod. 
Where  frequent  analyses  are  made 
the  Lung1  Nitrometer  method  is  bet¬ 
ter.  A  nitrometer  modified  espec¬ 
ially  for  the  use  of  the  determination 
of  nitrate  in  saltpeter  is  here  illus¬ 
trated.  The  Nitrometer  “A”  and 
the  leveling  tube  “B”  are  filled  with 
mercury.  From  a  twenty  gram  sam¬ 
ple  which  has  been  dried  at  110°  to 
constant  weight  as  nearly  as  is  pos¬ 
sible  0.35  grams  is  put  into  a  weigh¬ 
ing  tube.  This  is  then  accurately 
weighed  and  the  contents  shaken 
into  the  entry  tube  “C.”  The  weigh¬ 
ing  tube  is  again  weighed  and  the 
difference  in  weight  is  the  grams 
sample  employed.  This  should  be 
close  to  0.35  grams  so  that  the  gas 
evolved  will  be  more  than  100  cc.  and  less  than  130  cc.  at 
ordinary  temperature'  and  pressure. 

About  .5  cc.  wate  r  is  then  poured  in  and  the  solution 
and  crystals  (after  a  minute’s  standing)  are  drawn  into 
the  measuring  tube  by  opening  the  three-way  cock  into 
the  entry  tube  “0”  and  lowering  the  leveling  bulb  cau¬ 
tiously.  The  cup  is  washed,  using  less  than  1  cc.  of  water, 
and  about  15  cc.  of  strong  sulfuric  acid  is  admitted 
through  the  entry  tube  into  the  measuring  tube.  (More 
than  iy2  cc.  H20  renders  the  acid  too  dilute,  and  the 


TRANS. AM  CER  SOC.  V0L.XII  LANDRUM 


1  Berichte  1885,  18,  1391. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


25 


mercury  is  attacked) .  After  the  cock  is  closed  the  leveling 
tube  is  placed  in  a  clamp,  the  measuring  tube  is  thor¬ 
oughly  shaken  and  the  following  reaction  takes  place : 

Nn02+H2C204  :  2H20+H2S04  =  MnS04+2C02+4H20. 

The  measuring  tube  is  now  placed  in  clamp  on  a  level 
with  the  levelling  tube  and  solution  is  allowed  to  cool 
for  an  hour. 

The  tube  is  then  accurately  leveled,  allowing  one 
division  of  mercury  for  each  six  and  one-half  divisions  of 
acid,  and  the  gas  volume  read  off.  The  temperature  and 
barometric  pressure  are  read  and  the  gas  corrected  to 
standard  conditions.  Each  cc.  NO  gas  corresponds  to 
.0037986  g.  NaN03  or  .003845  g.  KN03. 

The  Analysis  of  Cryolite. 

Cryolite  is  a  mineral  occurring  in  large  quantities  in 
Greenland,  and  is  the  sodium  salt  of  hydrofluo-aluminic 
acid,  Na3AlF6.  It  is  used  in  enamels  and  is  fused,  finely 
ground  with  the  frit  giving  it  a  milky  opaqueness  which 
enamellers  call  “body.”  It  is  a  very  expensive  material 
and  is  most  always  far  from  pure,  either  being  deliberately 
adulterated  or  merely  naturally  impure. 

Methods  used  by  most  chemists  for  its  analysis  are 
at  the  best  crude.  The  direct  determination  of  the  fluorine 
is  the  only  satisfactory  means  of  properly  grading  it.  The 
method  used  for  cryolite  is  exactly  the  same  as 
that  employed  in  the  analysis  of  fluorine-bearing  enamel 
as  given  in  the  beginning  of  this  article,  except  that  one 
gram  of  the  cryolite  is  finely  ground  with  about  three 
grams  (accurately  weighed)  of  pure  silica,  and  this  mix¬ 
ture  is  fused  with  about  eight  grams  of  equal  parts  of 
sodium  carbonate  and  potassium  carbonate.  In  determin¬ 
ing  the  silica  in  the  cryolite,  this  silica  which  has  been 
added  must  be  deducted  from  that  found. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


The  alkalies  are  determined  by  the  method  of  J.  Law¬ 
rence  Smith1  from  a  gram  sample  linely  powdered. 

Combination  of  Results.  All  soda  is  combined  with 
sufficient  fluorine  to  form  sodium  fluoride  (NaF2).  The 
remainder  of  the  fluorine  is  combined  with  aluminum  as 
aluminum  fluoride  (A1F3).  The  remainder  of  the  alumi¬ 
num  is  calculated  as  alumina  ( ALCL ) . 

The  Analysis  of  Fluospar. 

Fluorspar  is  analyzed  especially  for  its  fluorine  con¬ 
tent  by  the  same  method  as  that  given  under  Cryolite.  It 
is  a  material  seldom  adulterated  and  a  mere  fusion  with 
six  times  the  Aveight  of  sodium  carbonate,  the  taking  to 
dryness  with  hydrochloric  acid  as  in  ordinary  silicate 
analysis,  the  removal  of  iron  and  alumina  as  hydroxide 
with  ammonia,  and  the  precipitation  with  ammonium 
oxalate  of  the  calcium  and  its  final  weighing  as  calcium 
oxide,  is  sufficient  in  most  cases.  All  the  calcium  may  be 
calculated  as  OaF2.  The  determination  of  the  fluorine, 
how  ever,  is  of  course  the  only  exact  method  of  accurately 
grading  this  material. 

The  approximate  method  for  determining  the  fluorine 
is  as  follows: 

Approximate  Method  foi'  Fluorine.  About  one  gram 
of  sample  finely  ground  and  accurately  weighed  is  in¬ 
timately  mixed  in  agate  mortar  w  ith  about  the  same  quan¬ 
tity  of  pure  silica.  The  whole  is  transferred  to  a  250  cc. 
Ehrlenmeyer  flask — rinsing  the  mortar  with  more  silica. 
The  flask  is  weighed  and  a  weighed  quantity  of  concen¬ 
trated  sulfuric  acid  is  added.  The  record  should  now- 
show  the  weight  of  flask,  silica  and  acid.  The  flask,  is 
gently  heated  and  the  loss  of  Aveight  is  calculated  as  sili¬ 
con  fluoride. 

Iron.  For  use  in  light  colored  enamels  the  iron  con¬ 
tent  of  the  fluorspar  is  important.  Five  grams,  finely 

1  Am.  Jour.  Science  (2)  50,  p.  269.  Treadwell-Hall  Anal.  Chem.,  Vol.  II, 
p.  394. 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


27 


ground,  are  heated  in  a  platinum  disli  with  an  excess  of 
sulfuric  acid  as  long  as  hydrofluoric  acid  is  given  off. 

After  cooling  it  is  diluted  with  100  cc.  of  water,  and 
after  reducing  by  drawing  through  a  Jones  Reductor  the 
solution  is  titrated  with  N/10  potassium  permanganate 
solution. 

Accurate  Method  for  Fluorine.  The  fluorine  may  be 
accurately  determined  by  the  following  method : 

One  gram  sample  (ground  to  pass  through  200  mesh 
sieve)  is  mixed  with  three  grams  silica  and  three  grams 
each  sodium  carbonate  and  potassium  carbonate  in  a 
platinum  crucible.  Heat  gradually  until  it  is  in  quiet 
fusion.  The  thin  liquid  fusion  soon  changes  to  a  thick 
paste  or  only  sinters  somewhat.  The  reaction  is  complete 
when  there  is  no  further  evolution  of  carbon  dioxide. 

After  fusion  the  melt  is  treated  with  water  and  after 
cooling  the  insoluble  residue  is  filtered  off  and  thoroughly 
washed.  The  solution  contains  all  fluorine  and  consider¬ 
able  silica.  Remove  the  silica  by  adding  four  grains  solid 
ammonium  carbonate.  Heat  liquid  at  40° C.  for  some 
time  and  let  stand  over  night.  Filter  in  morning  and  wash 
with  ammonium  carbonate  water. 

Evaporate  on  water  bath  almost  to  dryness  in  plati¬ 
num  dish  (keep  covered,  as  liquid  foams).  Dilute  with  a 
little  water.  Add  a  few  drops  of  phenolphthalein.  Add 
dilute  HC1  until  colorless.  Heat  on  steam  bath  and  color 
will  return.  Cool  and  repeat  operation  until  1.5  cc.  dou¬ 
ble  normal  HC1  is  sufficient  to  make  colorless.  Remove 
last  traces  silica  by  treating  the  solution  with  a  solution 
of  moist  zinc  oxide  in  ammonia  water.  Roil  until  am¬ 
monia  is  completely  expelled.  Filter  off  silica  and  zinc 
oxide  and  wash  with  water. 

Precipitate  fluorine  as  calcium  fluoride  and  calcium 
carbonate  by  adding  an  excess  of  calcium  chloride.  Filter, 
using  blue  ribbon  paper,  and  wash  thoroughly  with  hot 
water.  Dry  precipitate  on  funnel.  Transfer  as  much  as 
possible  to  a  platinum  crucible.  Burn  filter  and  add  ash. 
Ignite  contents  of  crucible. 


28  ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


After  cooling  the  mass  is  covered  with  a  slight  excess 
of  dilute  acetic  acid  (this  changes  the  calcium  oxide  to 
soluble  acetate.)  Evaporate  to  dryness  on  steam  bath. 
Take  up  with  water.  Filter,  wash  and  dry.  Transfer  most 
of  precipitate  to  weighed  platinum  crucible.  Burn  filter 
paper.  Add  asli.  Ignite  and  weigh  as  calcium  fluoride, 
CaF2.  To  confirm  the  results  add  cautiously  little  concen¬ 
trated  sulfuric  acid.  Evaporate  off  excess  sulfuric  acid, 
ignite  and  weigh  as  calcium  sulfate. 

The  Analysis  of  Oxides  of  Antimony. 

Arsenic.  One  gram  of  oxide  of  antimony  is  dis¬ 
solved  in  10  cc.  of  strong  hydrochloric  acid — at  as  low  a 
temperature  as  possible.  The  solution  is  then  cooled  and 
packed  in  ice  and  the  arsenic,  which  is  almost  invariably 
present,  is  removed  by  passing  through  H2S  for  several 
hours.  The  As2S3  is  filtered  off  in  a  weighed  Gooch  cru¬ 
cible,  washed  first  with  OS2  and  alcohol  then  with  concen¬ 
trated  hydrochloric  acid  and  dried  at  100°,  and  weighed 
as  As2S3. 

Antimony.  The  filtrate  from  above  is  put  into  250  cc. 
volumetric  flask,  rinsing  the  beaker  well  with  concentrated 
hydrochloric  acid  and  an  equal  part  of  water.  All  the  H2S 
is  removed  by  passing  through  a  current  of  air.  Five 
grams  of  tartaric  acid  are  added  and  the  liquid  diluted  to 
the  mark. 

Twenty- five  cc.  of  the  solution  are  measured  out  with  a 
pipette  and  are  neutralized  with  dry  sodium  bi  carbonate — 
keeping  covered  to  avoid  loss — finally  a  pinch  of  sodium 
bi-carbonate  and  a  cubic  centimeter  of  clear  starch  solu¬ 
tion  is  added  and  the  mixture  is  titrated  with  N/10  iodine 
solution. 

1  cc.  N/10  Iodine  =  0.0060  grams  Sb. 

The  Analysis  of  Oxide  of  Cobalt. 

Arsenic.  One  gram  finely  pulverized  sample  is  fused 
at  low  heat  with  ten  grams  bisulfate  of  potassium  for  three 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS.  29 


hours.  The  melt  is  extracted  with  water  acidified  with 
sulfuric  acid  and  the  arsenic  is  precipitated  from  the  warm 
acid  solution  with  H2S,  collected  in  a  weighed  Gooch 
crucible,  washed  with  water  containing  II2S  and  dried  at 
100°  for  one  hour  and  weighed  as  As2S3. 

Cobalt.  The  filtrate  from  above  is  boiled,  and  at  the 
same  time  air  is  drawn  through  to  remove  the  H2S,  and  it 
is  then  treated  by  Fisher’s  Potassium  Nitrite  method1  to 
separate  the  cobalt  and  the  nickel. 

The  concentrated  solution  containing  salts  of  both 
metals  is  treated  with  pure  potassium  hydroxide  to  alka¬ 
line  reaction,  made  slightly  acid  with  acetic  acid,  and  to 
this  a  concentrated  solution  of  pure  potassium  nitrite 
that  has  been  made  slightly  acid  with  acetic  acid  is  added. 
After  vigorous  stirring,  the  mixture  is  allowed  to  stand 
twenty- four  hours  in  a  warm  place.  Before  filtering,  a 
little  of  the  clear  solution  is  pipetted  off  and  treated  with 
more  potassium  nitrite  to  see  if  the  precipitation  of  the 
cobalt  has  been  complete.  If  a  precipitate  is  formed,  the 
whole  solution  is  treated  with  more  potassium  nitrite  and 
again  allowed  to  stand  until  complete  precipitation  is  ef¬ 
fected.  The  precipitate  is  then  filtered  and  washed  with 
a  barely  acid  5  per  cent  solution  of  potassium  nitrite  until 
1  cc.  of  the  filtrate,  after  being  boiled  with  hydrochloric 
acid  and  treated  with  caustic  potash  and  bromine  water, 
no  longer  gives  a  black  precipitate  of  nickelic  hydroxide. 
The  cobalt  precipitate  is  then  transferred  to  a  porcelain 
dish,  covered,  and  hydrochloric  acid  is  gradually  added 
until  there  is  no  further  evolution  of  nitric  oxide,  and 
after  filtering,  the  cobalt  is  precipitated  by  means  of  caus¬ 
tic  potash  and  bromine  water. 

The  precipitate  is  filtered  off,  using  blue  ribbon  filter 
paper,  dried,  and  ignited.  After  cooling  it  is  treated  with 
water  in  order  to  remove  the  small  amount  of  alkali  which 
is  always  present,  after  which  the  residue  is  ignited  in  a 
stream  of  hydrogen  and  weighed  as  metal.  After  weigh- 


1  Treadwell,  Vol.  II,  p.  130. 


30 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


ing,  the  metal  is  disolved  in  hydrochloric  acid,  evaporated 
to  dryness,  the  dry  mass  moistened  with  hydrochloric  acid, 
then  treated  with  water,  and  the  small  residue  of  silicic 
acid  is  filtered  off.  This  residue  is  ignited  and  its  weight 
subtracted  from  that  obtained  after  the  ignition  in 
hydrogen. 

Nickel.  The  filtrate  containing  the  nickel  is  treated 
with  hydrochloric  acid  until  the  nitrite  is  completely  de¬ 
composed,  and  the  nickel  is  precipitated  with  potassium 
hydroxide  and  bromine  water  as  brownish-black  nickel ic 
hydroxide  [ M  ( OH )  3.  ] 

The  precipitate — which  seldom  contains  more  than 
ten  milligrams  of  nickel — is  washed  with  hot  water,  col¬ 
lected  on  a  filter  and  is  dried,  ignited  separately  from 
the  filter,  and  weighed  as  XiO,  in  which  form  it  was  proba¬ 
bly  present  in  the  oxide. 

Steel  Plate. 

The  steel  best  adapted  for  enameled  ware  is  of  very 
low  carbon  value  and  extremely  low  in  the  other  impuri¬ 
ties,  in  fact,  the  nearer  pure  iron  the  better.  Of  the  steel 
plate  used  by  the  Columbian  Enamelling  and  Stamping 
Company,  the  best  satisfaction  was  obtained  from  those 
giving  the  following  analysis: 

Sulfur  from  .040%  to  .050%  ;  phosphorous  from 
.030%  to  .090%  ;  silica  less  than  .01  %  ;  manganese  from 
.060%  to  .040%,  and  carbon  less  than  0.10%.  The  sheets 
must  be  of  an  even  gauge  for  seamless  drawn  work  and  of 
a  dark  soft  quality,  which  allows  them  to  be  drawn  with¬ 
out  tearing.  When  the  vessel  is  made  without  drawing  and 
sheets  are  used  flat,  this  evenness  of  gauge  is  not  so  much 
of  object.  The  grain  in  all  cases  must  be  as  open  as  pos¬ 
sible.  The  sheet  must  be  Ioav  in  carbon  and  sulfur,  as 
these  develop  gases  at  temperatures  of  the  muffle,  which 
would  cause  the  enamel  to  peel  off. 

Samples  of  the  steel  plate  are  obtained  from  drillings 
taken  from  eight  or  ten  sheets  stacked  in  a  pile,  and 


ANALYSIS  FOR  ENAMEL  AND  ENAMEL  RAW  MATERIALS. 


31 


drilled  holes  are  run  every  two  inches  on  the  diagonal  of 
the  plate.  Drillings  are  sampled  down  to  twenty-five 
grams,  which  are  kept  in  stoppered  bottles.  The  method 
of  analysis  is  that  commonly  employed  by  steel-works 
chemists,  and  can  easily  be  found  in  print  elsewhere,  and 
for  that  reason  will  not  be  given  here. 


